This research study investigated the relationship between high school principals. perceptions of their leadership and the implementation of the Rhode Island diploma system. The study also explored the changing nature of the role of principal in relation to the Proficiency Based Graduation Requirements (PBGR) and leadership skills used by practicing principals (RIDE, 2011). In 2004 Rhode Island adopted new regulations for high schools that specified the Proficiency Based Graduation Requirements. The PBGR system has challenged principals to plan, design, and develop structures and strategies to achieve full diploma system implementation. The self-efficacy regarding leadership competence of the principal is integral for a school to achieve full implementation of the PBGR system (Bandura, 1995; RIDE, 2011; Tschannen-Moran & Gareis, 2004). A sequential mixed-method research design was employed (Creswell & Plano-Clark, 2007). High school principals (N = 37) in Rhode Island were surveyed using the Principal Leadership and the RI Diploma System questionnaire. A focus group of high school principals (N = 5) provided a deeper understanding of the quantitative findings. Descriptive statistics, "t"-tests, and ANOVA's were used to compare dimension-level means with demographic response items (Huck, 2008). Qualitative data analysis was conducted through a systemic coding of themes (Krippendorf, 2004). The quantitative results indicated that the high school principals' self-perceived leadership competence and the principals' sense of self-efficacy regarding tasks associated with the diploma system are positively correlated with diploma system implementation. It was also noted that self-efficacy was positively correlated with self-perceived leadership competence, and that urban principals had a lower sense of self-efficacy regarding leadership competence in comparison to suburban and urban-ring principals (Creswell, 2009; Krippendorf, 2004). Qualitative results indicated principals understood the key leadership characteristics needed to achieve successful implementation of the diploma system. Principals also related that the nature and scope of the mandated reforms has required the principal to develop expanded leadership competence (Marzano, Waters, & McNulty, 2005). The results of this study provide for greater understanding of leadership in relation to the PBGR system. Recommendations are provided for principals to develop and expand their leadership competence and network with fellow principals. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]